1. Field of the Invention
The invention relates to a crank assembly, more particularly to a crank assembly for a bicycle.
2. Description of the Related Art
Referring to FIG. 1, a conventional crank assembly for a bicycle is shown to comprise a drive plate 11 with through-holes formed therethrough, and an elongated crank arm 10 which has an upper end portion formed integrally with the drive plate 11, and a lower end portion formed with a threaded hole 13 in which a pedal of the bicycle is mounted. The drive plate 11 has a central hole of rectangular cross section which permits the fixed rotating shaft 12 of a sprocket 1 of the bicycle to extend therethrough in such a manner that the drive plate 11 can rotate synchronously with the sprocket 1. A plurality of screws 111 are inserted through the though-holes of the drive plate 11 so as to be threaded in the threaded holes of the drive plate 11 and the sprocket 1, thereby completing assembly of the conventional crank assembly on the sprocket 1. When the pedal is actuated, the sprocket 1 rotates to drive the bicycle.
Note that it is difficult to produce the conventional crank assembly as a unitary piece due to the complicated structure thereof. The conventional crank assembly is made of aluminum alloy. Since the mold, which is used in the formation of the conventional crank assembly, has a plurality of intercommunicated cavities, bubbles of air are often entrapped within the aluminum alloy during the molding operation, thereby resulting in uneven outer surfaces of the conventional crank assembly and correspondingly, in poor quality thereof.